Oxygen Sensor Testing and Replacement (DIY)
Ok here ya go......
Do you mean the O2 (oxygen) sensor? The oxygen sensor is the device that the engine control computer uses to monitor the amount of oxygen in the exhaust gas stream. The information gathered is used to fine-tune the air/fuel ratio so that the engine can run with the greatest efficiency possible in all conditions.
Can you check it yourself? The answer is yes, if you have the right equipment, tools, and knowledge. I will do my best to describe the process of testing and replacing the oxygen sensor.
Testing (3 methods)
The process of testing: Generally the best method of testing is by using an oscilloscope or Diagnostic Scan Tool (DST). Also some newer Digital Multi-Meters can function as oscilloscopes for testing.
Note: While testing, Diagnostic Trouble Codes may be set off, so be sure to clear them before re-testing the sensor. Common DTC's include:
- Open in the O2 sensor circuit
- Constant low or high voltage in the circuit
- Other problems could set off a DTC
Also, testing ONLY the O2 sensor is not a proper method for testing because the voltage output signal may be affected. After testing the sensor, be sure to check the fuel delivery and engine management system as well before assuming the problem is the O2 sensor.
I have posted instructions for regular, 3-wire, and 4-wire sensors. I believe Acura Vigor's utilize the 4-wire sensor, so you can go straight to the "4-wire sensor" testing section below.
1. Perform a visual inspection of the sensor. Black deposits may indicate it is running rich. Also, there are various causes for sensor failure so make sure to fix the problem before installing a new one to make sure the new sensor will last and not succumb to the same fate as the last. Then locate the pigtail connector
2. Start engine and allow it to warm up to normal operating temperature, then turn engine off.
3. Use a DVOM (Digital Volt-ohmmeter) set to read 100 - 900 mV (mill volts) DC to backprobe the positive DVOM lead to one of the unidentified terminals and attach the negative lead to an engine ground.
4. Have a second person restart the engine and allow it to idle.
5. Check voltage.
6. If no voltage registers, check leads for proper connection. If there is still no voltage, change the positive lead to backprobe the second terminal.
7. If voltage is present, the positive meter lead is properly connected to the SOUT terminal. The other terminal is the SGND terminal. If there is still no voltage, either the O2 sensor is bad or the terminals are still not properly connected. (Make sure contact areas are clean).
8. Have second person turn engine off.
9. Label the SOUT and SGND terminals so you know which is which.
3-wire sensors (3-wire sensors are HO2 sensors)
On 3-wire sensors, one of the connector terminals is the SOUT, one is the HPWR, and one is the HGND. The SGND is achieved through your exhaust system, as with the 1-wire O2 sensor.
1. To positively identify the 3 different terminals, locate the O2 sensor and its pigtail connector.
2. Disengage the sensor pigtail connector from the harness connector.
3. Using the DVOM again set to read 12 volts this time, attach the DVOM ground to an engine ground.
4. Have a second person turn the ignition to on, but DO NOT start the engine.
5. Probe the 3 terminals in the harness connector. The one that shows 12 volts of power is the HPWR terminal. If you are able to find the HPWR terminal, note which sensor connector terminal is the HPWR, then match the harness connector to the sensor pigtail connector. Label the pigtail connector as HPWR. If none of the terminals show 12 volts, then test the heater relay or fuse. Then repeat the previous steps along with the next step.
6. Start engine and allow it to warm up to operating temperature, then turn engine off.
7. Have second person turn ignition off.
8. Use the DVOM set to measure ohms (resistance) and attach one of the terminal leads to the HPWR terminal of the sensor pigtail connector. Use the other lead to probe the other 2 terminals of the sensor pigtail connector, only do one at a time. The terminal that shows a continuous reading is the HGND terminal. The remaining one by default is the SOUT terminal.
9. The 3 terminals should all be identified by now on the sensor pigtail connector (and labeled).
4-wire sensors (4-wire sensors are HO2 sensors)
On 4-wire sensors, one terminal is the SOUT, one is the SGND, one is the HPWR, and one is the HGND.
1. To identify the terminals, locate the O2 sensor and pigtail connector.
2. Disengage the sensor pigtail connector from harness connector.
3. Use the DVOM set to read 12 volts and attach it to a good ground.
4. Have second person turn the ignition to on, but DO NOT start the engine.
5. Probe all 4 terminals. The one that shows continuous 12 volts is the HPWR terminal. Then note which sensor connector terminal is the HPWR. If none register, check to make sure a good connection is made.
6. Have second person turn ignition off.
7. Use the DVOM set to ohms to probe the other 3 terminals. The one that registers is the HGND terminal. If continuity was found at two of the other terminals or if no continuity was found in any of the remaining terminals, it is likely the oxygen sensor is bad.
8. Re-attach the sensor pigtail connector to the harness connector.
9. Start the engine and allow to warm up to normal operating temperature, then turn engine off.
10. Use the DVOM set to read 100-900 mV (mill volts) DC to backprobe the negative DVOM lead to one of the unidentified terminals and the positive lead to another unidentified terminal.
11. Have second person restart the engine and allow it to idle.
12. Check the DVOM for voltage. If there is no voltage, check leads for good contact. If no voltage is still evident at either of the terminals, the terminals were either incorrectly marked or the sensor is bad. If voltage is shown but polarity is reversed, turn engine off, switch the leads, and then restart the engine so the polarity is correct. If voltage is shown and polarity is correct, the positive DVOM lead is connected to the SOUT and the negative to the SGND.
Wow I really need to take a break.......... Okay, I'm back
After checking your sensor and you find it to be defective, here is how to go about replacing it.
Remember: The sensors have a pigtail and connector. It is important not to remove these from the sensor. If these parts are damaged, they could affect the sensor's performance. Keep these clean and grease-free. Do not use cleaning products on or around the sensor!! Also, the sensor may be more difficult to remove if the engine temperature is too low and using too much force in removal may damage the threading in the exhaust pipe/manifold.
1. With the engine off and the ignition in the off position, disconnect the negative battery cable. (Remember, the Vigor is equipped with an anti-theft radio that automatically disables itself if the battery is disconnected. Make sure you have the 5 digit code to enter in the radio upon reconnection of the battery cable to allow it to work again).
2. Locate the oxygen sensor. It comes out from the exhaust manifold/pipe and looks similar to a spark plug.
3. Unplug the electrical connector to the sensor.
4. Unscrew the sensor very carefully! You can buy wrenches that are specifically made for removing these sensors. They make the job easier and decrease the risk of damage during removal.
5. After the removal, be careful to keep the tip clean if you are going to re-use it. Do NOT wash it!
6. Apply an anti-seize compound to the bolt threads but make sure none of it comes in contact with the tip.
7. Install the sensor.
8. Make sure the connection is tight and re-connect the electrical connector.
9. Re-connect the previously removed negative battery cable.
(Some late-model Acuras have two O2 sensors, but you don't need to worry about that for your particular application).
If you want to do this job yourself, I believe I have provided all the necessary information in order to do so. If not, hopefully it will help someone else (it would be a shame to have written all of this for nothing!). Good Luck, let us know how it turns out.
Last edited by AcuraVigorOwner; 05-09-08 at 08:28 PM.